Methanol

From New World Encyclopedia
Revision as of 01:36, 1 November 2008 by AdminBot (contribs)
Jump to: navigation, search
Methanol
MethanolMethanol
General
Systematic name methanol
Other names hydroxymethane
methyl alcohol
wood alcohol
carbinol
Molecular formula CH3OH
SMILES CO
Molar mass 32.04 g/mol
Appearance colorless liquid
CAS number [67-56-1]
Properties
Density and phase 0.7918 g/cm³, liquid
Solubility in water Fully miscible
Melting point –97 °C (176 K)
Boiling point 64.7 °C (337.8 K)
Acidity (pKa) ~ 15.5
Viscosity 0.59 mPa·s at 20 °C
Structure
Molecular shape Tetrahedral and Bent
Dipole moment 1.69 D (gas)
Hazards
MSDS External MSDS
EU classification Flammable (F)
Toxic (T)
NFPA 704

NFPA 704.svg

3
1
0
 
R-phrases R11, R23/24/25,
R39/23/24/25
S-phrases S1/2, S7, S16,
S36/37, S45
Flash point 11 °C
Flammable limits
in air (by volume)
6.72% - 36.50%
RTECS number PC1400000
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Related alkanols ethanol
butanol
Related compounds chloromethane
methoxymethane
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)

Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha, or wood spirits, is the simplest alcohol. Its chemical formula is CH3OH. It is a colorless, volatile, flammable liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). It is poisonous and should be handled with care.

Methanol is used as a solvent, fuel, and antifreeze. Its main use, however, is in the production of other chemicals. About 40 percent of methanol is converted to formaldehyde, which in turn is used for products such as plastics, paints, explosives, and textiles. It is added to ethanol to produce what is called denatured alcohol (that is, ethanol that has been rendered toxic), which has various uses in industry.[1]

Contents

Natural occurrence

Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria. As a result, there is a low level of methanol vapor in the atmosphere. Over the course of several days, atmospheric methanol is oxidized by oxygen with the help of sunlight, to generate carbon dioxide and water.

History

In their embalming process, the ancient Egyptians used a mixture of substances, including methanol, which they obtained from the pyrolysis of wood. Pure methanol, however, was first isolated in 1661 by Robert Boyle, who called it spirit of box, because he produced it via the distillation of boxwood. It later became known as pyroxylic spirit. In 1834, the French chemists Jean-Baptiste Dumas and Eugene Peligot determined its elemental composition. They also introduced the word methylene to organic chemistry, forming it from Greek methy = "wine" + hŷlē = wood (patch of trees). Its intended origin was "alcohol made from wood (substance)," but it has Greek language errors. The term "methyl" was derived in about 1840 by back-formation from methylene, and was then applied to describe "methyl alcohol." This was shortened to "methanol" in 1892 by the International Conference on Chemical Nomenclature. The suffix -yl used in organic chemistry to form names of radicals, was extracted from the word "methyl."

In 1923, the German chemist Matthias Pier, working for BASF developed a means to convert synthesis gas (a mixture of carbon oxides and hydrogen) into methanol. This process used a zinc chromate catalyst, and required extremely vigorous conditions—pressures ranging from 30–100 MPa (300–1000 atm), and temperatures of about 400°C. Modern methanol production has been made more efficient through use of catalysts (commonly copper) capable of operating at lower pressures.

The use of methanol as a motor fuel received attention during the oil crises of the 1970s due to its availability and low cost. Problems occurred early in the development of gasoline-methanol blends. As a result of its low price some gasoline marketers over blended. Others used improper blending and handling techniques. This led to consumer and media problems and the last time out of methanol blends. However, there is still a great deal of interest in using methanol as a neat (unblended) fuel. The flexible-fuel vehicles currently being manufactured by General Motors, Ford, and Chrysler can run on any combination of ethanol, methanol and/or gasoline. Neat alcohol fuels will become more widespread as more flexible-fuel automobiles are manufactured.

In 2006, astronomers using the MERLIN array of radio telescopes at Jodrell Bank Observatory discovered a large cloud of methanol in space, 300 billion miles across.

Properties

At ordinary temperature and pressure, methanol is a liquid with a density of 0.7918 g/cm³. It has a melting point –97 °C, a boiling point of 64.7 °C, and a flash point of 11 °C.

Methanol burns in air to form carbon dioxide and water:

2 CH3OH + 3 O2 → 2 CO2 + 4 H2O

A methanol flame is almost colorless. Care should be exercised around burning methanol to avoid burning oneself on the almost invisible fire.

Methanol is corrosive for some metals, including aluminum. Although a weak acid, it attacks the oxide coating that normally protects the aluminum from corrosion:

6 CH3OH + Al2O3 → 2 Al(OCH3)3 + 3 H2O

The aluminum methoxide produced is soluble in methanol. As a result, the aluminum surface is cleaned of its oxide coating and then is readily oxidized by some dissolved oxygen. Also, the methanol can act as an oxidizer:

6 CH3OH + 2 Al → 2 Al(OCH3)3 + 3 H2

This reciprocal process effectively fuels corrosion until either the metal is eaten away or the concentration of CH3OH becomes negligible.

Artificial production

Methanol is often called wood alcohol because it was once produced chiefly as a by-product of the destructive distillation of wood. It is now produced synthetically by a multi-step process. In brief, natural gas and steam are reformed in a furnace to produce hydrogen and carbon monoxide. This step is endothermic (it absorbs heat). Next, hydrogen and carbon monoxide gases are made to react under pressure in the presence of a catalyst, to produce methanol. This synthesis step is exothermic (it releases heat).

Today, synthesis gas is most commonly produced from the methane component in natural gas rather than from coal. Three processes are commercially practiced. At moderate pressures of 1 to 2 MPa (10–20 atm) and high temperatures (around 850 °C), methane reacts with steam on a nickel catalyst to produce syngas according to the chemical equation:

CH4 + H2OCO + 3 H2

This reaction, commonly called steam-methane reforming or SMR, is endothermic and the heat transfer limitations place limits on the size of the catalytic reactors used. Methane can also undergo partial oxidation with molecular oxygen to produce syngas, as the following equation shows:

2 CH4 + O2 → 2 CO + 4 H2

this reaction is exothermic and the heat given off can be used in-situ to drive the steam-methane reforming reaction. When the two processes are combined, it is referred to as autothermal reforming. The ratio of CO and H2 can be adjusted by using the water-gas shift reaction,

CO + H2OCO2 + H2,

to provide the appropriate stoichiometry for methanol synthesis.

The carbon monoxide and hydrogen then react on a second catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper, zinc oxide, and alumina first used by ICI in 1966. At 5–10 MPa (50–100 atm) and 250 °C, it can catalyze the production of methanol from carbon monoxide and hydrogen with high selectivity

CO + 2 H2 → CH3OH

It is worth noting that the production of synthesis gas from methane produces 3 moles of hydrogen for every mole of carbon monoxide, while the methanol synthesis consumes only 2 moles of hydrogen for every mole of carbon monoxide. One way of dealing with the excess hydrogen is to inject carbon dioxide into the methanol synthesis reactor, where it, too, reacts to form methanol according to the chemical equation

CO2 + 3 H2 → CH3OH + H2O

Although natural gas is the most economical and widely used feedstock for methanol production, other feedstocks can be used. Where natural gas is unavailable, light petroleum products can be used in its place. The South African firm Sasol produces methanol using synthesis gas from coal.

Uses

  • The largest use of methanol by far is in making other chemicals. About 40 percent of methanol is converted to formaldehyde, and from that into products as diverse as plastics, plywood, paints, explosives, and permanent press textiles.
  • Methanol is also used as a solvent and as an antifreeze in pipelines and windshield washer fluid.
  • Methanol is used on a limited basis to fuel internal combustion engines, mainly by virtue of the fact that it is not nearly as flammable as gasoline. Methanol blends are the fuel of choice in open wheel racing circuits like Champcars, as well as in radio controlled model airplanes (required in the "glow-plug" engines that primarily power them), cars and trucks. Dirt circle track racecars such as Sprint cars, Late Models, and Modifieds use methanol to fuel their engines. Drag racers and mud racers also use methanol as their primary fuel source. Methanol is required with a supercharged engine in a Top Alcohol Dragster and, until the end of the 2005 season, all vehicles in the Indianapolis 500 had to run methanol. Mud racers have mixed methanol with gasoline and nitrous oxide to produce more power than gasoline and nitrous oxide alone. One of the drawbacks of methanol as a fuel is its corrosivity to some metals, including aluminum, noted earlier.
  • In addition to direct use as a fuel, methanol (or less commonly, ethanol) is used as a component in the chemical formation of biodiesel fuel.
  • When produced from wood or other organic materials, the resulting organic methanol (bioalcohol) has been suggested as renewable alternative to petroleum-based hydrocarbons. However, one cannot use BA100 (100 percent bioalcohol) in modern petroleum cars without modification.
  • Methanol is a traditional ingredient in methylated spirit or denatured alcohol.
  • During World War II, methanol was used as a fuel in several German military rocket designs, under name M-Stoff, and in a mixture as C-Stoff.
  • In some wastewater treatment plants, a small amount of methanol is added to wastewater to provide a food source of carbon for the denitrification bacteria, which convert nitrates to nitrogen.
  • In early 1970s, the methanol to gasoline process was developed by Mobil, which produces gasoline ready for use in vehicles. One industrial facility was built in New Zealand in the 1980s.
  • In the 1990s, large amounts of methanol were used in the United States to produce the gasoline additive methyl tert-butyl ether (MTBE). The 1990 Clean Air Act required certain major cities to use MTBE in their gasoline to reduce photochemical smog. However, by the late 1990s, it was found that MTBE had leaked out of gasoline storage tanks and into the groundwater in sufficient amounts to affect the taste of municipal drinking water in many areas. Moreover, MTBE was found to be a carcinogen in animal studies. In the resultant backlash, several states banned the use of MTBE, and its future production remains uncertain.
  • Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, allowing them to be miniaturized to an unprecedented degree. This, combined with the relatively easy and safe storage and handling of methanol may open the possibility of fuel cell-powered consumer electronics.
  • Other chemical derivatives of methanol include dimethyl ether, which has replaced chlorofluorocarbons as an aerosol spray propellant, and acetic acid.

Health and safety

Methanol can enter the body by ingestion, inhalation, or absorption through the skin. It is toxic after it is metabolized in the liver by the enzyme alcohol dehydrogenase to form formaldehyde, which in turn causes blindness by destroying the optic nerve.[2] Methanol ingestion can also be fatal because it can depress the central nervous system in the same manner as ethanol poisoning. Fetal tissue will not tolerate methanol. Dangerous doses will build up if a person is regularly exposed to vapors or handles the liquid without skin protection.

If methanol has been ingested, a doctor should be contacted immediately. The usual fatal dose is 100–125 mL (4 fl oz). Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. This is treated using ethanol or fomepizole.[3] Either of these drugs acts to slow down the action of alcohol dehydrogenase on methanol by means of competitive inhibition, so that it is excreted by the kidneys rather than being transformed into toxic metabolites.

The initial symptoms of methanol intoxication are those of central nervous system depression: headache, dizziness, nausea, lack of coordination, confusion, drowsiness, and, at sufficiently large doses, unconsciousness and death. The initial symptoms of methanol exposure are usually less severe than the symptoms resulting from the ingestion of a similar quantity of ethyl alcohol.

Once the initial symptoms have passed, a second set of symptoms arises 10–30 hours after the initial exposure to methanol: blurring or complete loss of vision, together with acidosis. These symptoms result from the accumulation of toxic levels of formate in the bloodstream, and may progress to death by respiratory failure. The ester derivatives of methanol do not share this toxicity.

Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of methanol. The result is known as methylated spirit or "meths" (in the UK). (The latter should not be confused with meth, a common abbreviation for methamphetamine.)

Pure methanol has been used in open wheel racing since the mid-1960s. Unlike petroleum fires, methanol fires can be extinguished with plain water (while methanol is less dense than water, they are miscible, and the addition of water will cause the fire to use its heat to boil the water). In addition, a methanol-based fire burns invisibly, unlike gasoline, which burns with thick black smoke. If a fire occurs on the track, there is no smoke to obstruct the view of fast approaching drivers. The decision to permanently switch to methanol in American IndyCar racing was a result of the devastating crash and explosion at the 1964 Indianapolis 500 which killed drivers Eddie Sachs and Dave MacDonald.

One concern with the addition of methanol to automotive fuels is highlighted by recent groundwater impacts from the fuel additive methyl tert-butyl ether (MTBE). Leaking underground gasoline storage tanks created MTBE plumes in groundwater that eventually adulterated well water. Methanol's high solubility in water raises concerns that similar well water contamination could arise from the widespread use of methanol as an automotive fuel.

See also

Notes

  1. The addition of a poison exempts industrial ethanol from the rather significant "liquor" taxes that would otherwise be levied, as ethanol is the essence of all potable alcoholic beverages.
  2. Methanol and Blindness Ask A Scientist. Retrieved September 22, 2007.
  3. January 2001. "Fomepizole in the Treatment of Poisoning," Pediatrics 107 (no. 1). Retrieved September 22, 2007.

References

  • McMurry, John. 2004. Organic Chemistry. 6th ed. Belmont, CA: Brooks/Cole. ISBN 0534420052.
  • Morrison, Robert T., and Robert N. Boyd. 1992. Organic Chemistry. 6th ed. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-643669-2.
  • Solomons, T.W. Graham, and Fryhle, Craig B. 2004. Organic Chemistry. 8th ed. Hoboken, NJ: John Wiley. ISBN 0471417998.

External links

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

Note: Some restrictions may apply to use of individual images which are separately licensed.

Research begins here...